This invention relates in general to golf balls and, more particularly, to a golf ball having an improved cover material.
The assembly of a golf ball generally involves molding a cover around a solid or wound core. Golf balls with wound cores are typically referred to as "three piece" balls because they consist of three basic components: (1) a solid or liquid-filled center; (2) rubber winding around the center, and (3) the cover. Similarly, solid cores are referred to as having a "two piece" construction, since they consist solely of a solid core and a cover. A third type of ball, known as a "one-piece" ball is also known in the art. As the name suggests, one piece balls are solid balls of homogeneous construction made by any conventional molding method suitable for the purpose.
The composition of the golf ball cover has proven to be a factor in overall golf ball performance. Historically, three piece balls had covers made of Balata, a natural resin obtained from trees in South and Central America and is essentially made up of transpolyisoprene.
Balata is still used today as a cover material because of the "click" and "feel" provided by the balata cover to the golfer. "Click" is the sound made by a golf club head when it hits the ball. "Feel" is the overall sensation transmitted to the golfer after hitting the ball. Balata covered golf balls are also used because of the excellent playability and good flight performance qualities. These balls give good flight distance and skilled golfers can impart desirable spin to the ball, enabling it to draw or fade in flight. Also, especially with high-lofted clubs, the backspin allows the ball to stop abruptly on approach shots.
However, balata type materials are expensive and the manufacturing procedures required are time-consuming, labor-intensive and therefore expensive.
The majority of modern golf balls use a two piece construction with covers made of a durable synthetic thermoplastic resin such as Surlyn, a product of E. I. DuPont de Nemours Company, Incorporated. Synthetic thermoplastic cover materials have been used with limited success. They are durable and produce satisfactory flight distance. Additionally, they are less costly to manufacture than balata covers. However, these materials are hard and therefore lack the "click" and "feel" of a balata ball. Moreover, it is not possible to impart to such balls the desirable spin characteristics required by skilled golfers. It is desirable, however, to utilize a synthetic cover material for improved process manufacturing and to increase desirability and resilience performance.
In an attempt to overcome the negative factors of the hard ionomer covers, DuPont introduced low modulus SURLYN ionomers in the early 1980's. These SURLYN ionomers have a flexural modulus of from about 3000 to about 7000 PSI and a hardness of from 25 to about 40 as measured on the Shore D scale - ASTM 2240. The low modulus ionomers are terpolymers of ethylene, methacrylic acid and n- or iso-butylacrylate, neutralized with sodium and zinc cations. E. I. DuPont De Nemours & Company has disclosed that the low modulus ionomers can be blended with other grades of previously commercialized ionomers of high flexural modulus of from about 30,000 to 55,000 PSI to produce balata-like properties.
The low modulus ionomers when used without blends produced covers with very similar physical properties to those of balata, including poor cut resistance. Worse, such covers tend to go "out-of-round" quicker than balata covers. Blending with hard SURLYN ionomers was found to improve these properties.
However, the relatively high cost of the soft SURLYN ionomers, together with the need to blend several grades of hard and soft ionomers to achieve the desired properties, militates against the use of soft/hard ionomer blends in the commercial manufacture of a golf ball.
Accordingly, it is an object of the present invention to provide a golf ball having a synthetic cover material.
Another object of the present invention is to provide an improved synthetic cover material for a golf ball.
It is another object of the present invention to provide a golf ball having a synthetic cover material that achieves the click, feel, playability and flight performance qualities of Balata covered golf balls.
A further object of the present invention is to provide a golf ball having a cover material that has improved process manufacturing as well as durability and resilience.